1. Field
This disclosure relates generally to non-volatile memories, and more specifically, to a built-in self trim mechanism for a reference current used in accessing non-volatile memories.
2. Related Art
Non-volatile memories typically rely upon a reference current (Iref) to distinguish whether a memory cell stores a zero value (e.g., less than Iref) or a one value (e.g., greater than Iref). In order to generate Iref, many non-volatile memory designs use a non-volatile memory bitcell as a reference cell. To ensure performance and reliability of the non-volatile memory array, the reference cell should be stable and not drift significantly over time. But, like many other semiconductor devices, a reference cell can be subject to environmental effects, as well as data retention errors and read disturb errors.
While reference cells are typically initially trimmed by a manufacturer of the non-volatile memory, there is no mechanism for the reference cell to be adjusted or re-trimmed in the field or by a customer incorporating the non-volatile memory in a subsequent product. Further, initial trimming of a reference cell can be a time-consuming procedure that utilizes equipment external to the non-volatile memory, or a package incorporating the non-volatile memory, and therefore can be costly in terms of resources and reductions in production volume. It is therefore desirable to have a built-in self-trim mechanism incorporated into non-volatile memory packages. It is further desirable that such a built-in self-trim mechanism be usable to both minimize reference drift in the field as well as aiding in initial trimming of the reference cell.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The figures are not necessarily drawn to scale.